Bleeding The Hydraulic Clutch On A Honda St1100

[BSJ]

Hi folks, I've been replacing leaky seals in the clutch slave cylinder and fitting new friction disc's to the clutch......and I have a problem bleeding the system. The only fluid in the system is in the master cylinder reservoir. The workshop manual says pull the lever in and quickly open and close the bleeder valve, then release and repeat.....which I did 100 times.....with no result! I put a vacuum on the bleeder to suck out the air but it wouldn't hold a vacuum.

It's like there is a problem with the master cylinder, but it was fine last Sunday.

Anyone have a clue?

[BigBikeBKK]

Oooh, that's a tough one... I've bled plenty of brakes, but never a hydraulic clutch... I imagine a clutch master cylinder is 'fairly' similar in design and operation to a brake master cylinder?

Assume you have the service manual for your ST1100?

Here's the Clutch Master Cylinder for your bike:

My only guess would be that something was mis-assembled when you replaced the leaking seals and re-assembled your clutch master cylinder. If it was me I'd take it all apart and rebuild it from scratch in hopes of discovering the problem. Also, I've found that bleeding hydraulic lines is always easier if you have an extra set of hands to help- one of you works the lever and the other takes care of the bleeder valve.

Good luck! Keep us posted on your progress!

Tony

[seedy]

Fill Master cylinder reservoir. Open slave cylinder bleeder screw a little. Wait for fluid to travel via gravity from master cylinder out the bleeder screw. Close Bleeder screw. Pump brake lever until pressure felt - this may take 3 or 4 squeezes. Hold pressure on lever. Slowly open bleeder screw until fluid runs out. Do not let brake lever hit grip. Close bleeder screw. Repeat until no air bubbles exit bleeder screw and lever is firm.

[BSJ]

Hi Tony, I have the manual but there is scant info on bleeding the brakes and clutch! Isn't it always the way!

I checked the net and one site said the return orifice may have become clogged if I dislodged some crap which has the effect of holding the fluid in the cylinder were items 1, 2, 3, 7, 11 & 19 are fitted. Which seems likely as cycling the lever produces no bubbles of air escaping into the reservoir.

Hi Seedy, if I could get the fluid to flow as you suggest...I wouldn't have a problem as I use a similar method to bleed the system!

[BigBikeBKK]

Hi Tony, I have the manual but there is scant info on bleeding the brakes and clutch! Isn't it always the way!

I checked the net and one site said the return orifice may have become clogged if I dislodged some crap which has the effect of holding the fluid in the cylinder were items 1, 2, 3, 7, 11 & 19 are fitted. Which seems likely as cycling the lever produces no bubbles of air escaping into the reservoir.

Hi Seedy, if I could get the fluid to flow as you suggest...I wouldn't have a problem as I use a similar method to bleed the system!

I hate it when my orifice gets clogged! (seriously though- take it all apart and clean it in kerosene, then reassemble one step at a time- with any luck it will work!)

[Lickey]

Hi folks, I've been replacing leaky seals in the clutch slave cylinder and fitting new friction disc's to the clutch......and I have a problem bleeding the system. The only fluid in the system is in the master cylinder reservoir. The workshop manual says pull the lever in and quickly open and close the bleeder valve, then release and repeat.....which I did 100 times.....with no result! I put a vacuum on the bleeder to suck out the air but it wouldn't hold a vacuum.

It's like there is a problem with the master cylinder, but it was fine last Sunday.

Anyone have a clue?

BSJ, the most foolproof method of bleeding hydraulics is to fill the master cylinder, open the bleed screw, wait for the fluid to dribble out, then pull in the lever, close the bleed screw,release the lever, and most important, watch to see if the fluid in MC goes down, if it does, open screw and repeat till air bubbles stop,if this doesnt work, then it could be a broken return spring in the MC, The way to test this is gently pull in the lever, and you should feel a slight resistant,

Vacunm method is ok on some systems but useless on others, you could back bleed the system, fill a pump type oil can with fluid, attach it via plastic pipe to the bleed screw and pump till MC is full, close screw and test,

just a few ideas for you before stripping it out again and possibly damaging the new seals,,

[BSJ]

Hi guys, all is good now. I sussed out the local Honda dealers service dept. They said to bleed the master cylinder by cracking the banjo fitting to the hose and using a sequence of one squeeze, bleed through the banjo over and over. It got a lot of fluid down the hose and a lot on the rags I had wrapped around the banjo fitting. After tightening the banjo fitting I bleed the slave cylinder....but I think there is still more air. Have another go at it tomorrow. But I have made progress. I started the old girl and pushed on the brake pedal as I pulled in the clutch and selected first......and she didn't stall! Yippee!